1. Field of the Invention
The present invention relates to a process for producing composite articles made of at least one hard and at least one soft component, with the hard component being based on a thermoplastic polyester and the soft component being a vulcanizate. The invention further relates to the articles obtained by this process.
2. Discussion of the Background
Frequently a single material cannot contribute all the properties which are demanded by an article. Such incompatible property combinations are, for example, simultaneously high strength and rubber elasticity or high hardness and stiffness on the one hand and skid resistance on the other hand.
To equip components with properties which cannot be contributed by a single material, they are composed of parts of various materials. A necessary prerequisite for the functionality of such articles is frequently strong adhesion between the parts of various materials.
The technical objective of generally bonding rubbers and thermoplastics strongly to one another is conventionally known and has hitherto been achieved in various, but not totally satisfactory ways.
Composite materials made of thermoplastically stiff and rubber-elastic molding materials are customarily put together by adhesive bonding, screwing, rivetting, mechanical interlocking or with the use of a coupling agent. Recently, interesting processes have been developed for producing a composite comprising molding compositions based on polyphenylene ethers (PPE) and certain rubbers which can be vulcanized by sulphur or peroxide (cf. EP-A-0 196 407 and EP-A-0 315 749).
The bond strength values achieved here are considerable.
It would be desirable, however, to also produce composite materials whose thermoplastic component, besides having a high geometric stability on heating, simultaneously has a good solvent resistance, stability to weathering and excellent sliding friction behavior.
Although it is known that the processes known from the cited applications are linked to certain unique and critical parameters, consideration could in principle be given to replacing the polyphenylene ether by other thermoplastics which better fulfil the specified requirements. However, it has been found that, for example, polyesters which are known to fulfil the above-mentioned requirements, do not allow satisfactory adhesion values to be achieved under the process conditions considered essential (see comparative experiments). It therefore appeared to be not possible to produce composites comprising thermoplastic polyesters and rubbers.
EP-A-0 375 867 describes a process for producing such composites in which the thermoplastic component comprises at least 30% of a reaction product of a thermoplastic polyester and a polyisocyanate. These reaction products have the disadvantage that at sufficiently high concentration of polyisocyanate they can only be injection-molded or extruded within a very narrow processing window.
German Application P 43 31 995.5 describes a process in which polyesters having an unimpaired processing behavior can be used in a composite with rubbers. This comprises using a hard component based on a thermoplastic polyester containing aliphatic double bonds, and, for the soft component, starting out from a rubber composition which is vulcanized in contact with the hard component under conventional vulcanization conditions and contains a particular functional silane.
However, improvements in the polyester processing behavior is being pursued.